Many gas lasers are excited by electron impact with a gas in a laser cavity. Electrons are accelerated by an electric field and transfer energy to the gas atoms or molecules by collisions. The process of raising electrons to an excited state is referred to as pumping. One typical configuration of such gas lasers is a transverse-electric-discharge configuration in which a pair of long electrodes (or a pair of linear arrays of electrodes) is located parallel to the optical axis of the gas laser and within the cavity of the laser so that the electron current flows transversely to the optical axis. U. S. Pat. No. 4,677,638 shows one example a transverse-electric-discharge gas laser.
Prior art gas lasers have typically relied on flash lamps; positioning electron sources outside the laser cavity proximate to a cavity window; and hot thermionic cathodes or secondary electron emission cold cathodes within the laser cavity as sources for stimulating laser radiation emissions. Gas lasers using flash lamps for stimulation require high current, high voltage power supplies to drive the flash lamp. In addition, only pulsed output is provided by the gas laser using the flash lamp. Electron sources outside the laser cavity require high energy power supplies to provide electrons with sufficient energy to penetrate the cavity window, e.g., a mylar sheet. Even if the energetic electrons start with a uniform energy, the electrons entering the cavity possess a broad energy distribution due to electron scattering in the window material. Some of the electrons reaching the gas in the cavity are above the ionization potential of the gas, and ultimately produce avalanche breakdown in the cavity.
When either hot or cold cathodes are used in a conventional gas laser, a high potential must be maintained across the laser cavity. The use of a hot thermionic cathode results in a number of problems. First, heat is transferred to both the laser gas and the laser envelope. Second, a hot thermionic cathode requires a heater power supply. Third, the active surface of the cathode evaporates during use. Fourth, a high potential is required across the cavity to accelerate the electrons from zero energy, which produces a significant electron energy distribution and associated avalanche breakdown in the gas. This results in ion production and associated sputtering of the hot cathode.
Problems are also associated with secondary emission cold cathodes. First, avalanche breakdown occurs because of the high potentials necessary for producing secondary electron emission from the cathode. In most cold cathode applications, avalanche effects are necessary for operation. Secondly, high energy ions sputter away the cathode. Third, the cathode itself must be large because the secondary electron coefficient is very small. This results in a very small number of electrons emitted from the cold cathode.
Gas lasers are often used in applications such as laser gyros. An ideal electron source for a laser gyro would provide electrons at a controllable energy, which is less than the ionization potential of the gas or gases in the laser cavity. In addition, the electron source would be powered from a compact light weight power supply, which advantageously would stimulate the production of electrons without excessive warmup times. A conventional gas laser using either a hot cathode or a secondary emission cold cathode results in problems similar to those described above. In addition, since there is a definite warmup time associated with hot cathodes, laser gyros employing a hot cathode must be continuously energized.
Although field emitter arrays have been used for high
speed electronics, ultrafast switches and spin polarized devices, e.g., U. S. Pat. Nos. 4,721,885, 4,578,614 and 4,835,438, respectively, and have also been used as electron sources in flat panel and cathode ray tube (CRT) displays, heretofore gas lasers have not been excited using such a technique.